FIG. 1 shows an exemplary network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) as a mobile communication system to which a related art and the present invention are applied. The E-UMTS system is a system that has evolved from the UMTS system, and its standardization work is currently being performed by the 3GPP standards organization. The E-UMTS system can also be referred to as a Long-Term Evolution (LTE) system.
The E-UMTS network can roughly be divided into an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and a Core Network (CN). The E-UTRAN generally comprises a terminal (i.e., User Equipment (UE)), a base station (i.e., eNode B), and an Access Gateway (AG) that is located at an end of the E-UMTS network and connects with one or more external networks. The AG may be divided into a part for processing user traffic and a part for handling control traffic. Here, an AG for processing new user traffic and an AG for processing control traffic can be communicated with each other by using a new interface. One eNode B may have one or more cells. An interface for transmitting the user traffic or the control traffic may be used among the eNode Bs. The CN may comprise an AG, nodes for user registration of other UEs, and the like. An interface may be used to distinguish the E-UTRAN and the CN from each other.
Radio interface protocol layers between the terminal and the network can be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based on three lower layers of an Open System Interconnection (OSI) standard model widely known in communications systems. A physical layer belonging to the first layer provides an information transfer service using a physical channel. A Radio Resource Control (RRC) layer located at the lowest portion of the third layer controls radio resources between the terminal and the network. For this purpose, the RRC layer allows RRC messages to be exchanged between the terminal and the network.
FIG. 2 shows radio interface protocol architecture between a terminal and E-UTRAN based on 3GPP radio access network standards. The radio interface protocol in FIG. 2 have horizontal layers comprising a physical layer, a data link layer and a network layer, and has vertical planes comprising a user plane for transmitting user traffic and a control plane for transmitting control signals. The protocol layers in FIG. 2 can be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based on three lower layers of an Open System Interconnection (OSI) standard model widely known in communications systems. Hereinafter, each layer in the radio protocol architecture in FIG. 2 will be described.
A first layer, as a physical layer, provides an information transfer service to an upper layer using a physical channel. The physical layer is connected to its upper layer, called a Medium Access Control (MAC) layer, via a transport channel. The MAC layer and the physical layer exchange data via the transport channel. Data is transferred via a physical channel between different physical layers, namely, between the physical layer of a transmitting side and the physical layer of a receiving side. The physical channel is modulated based on an Orthogonal Frequency Division Multiplexing (OFDM) technique, and utilizes time and frequency as radio resources.
The MAC layer located at the second layer provides a service to an upper layer, called a Radio Link Control (RLC) layer, via a logical channel. The RLC layer of the second layer supports reliable data transmissions. The function of the RLC layer may be implemented as a functional block in the MAC layer. In this case, the RLC layer may not exist. A Packet Data Convergence Protocol (PDCP) layer of the second layer, in the radio protocol user plane, is used to efficiently transmit IP packets, such as IPv4 or IPv6, on a radio interface with a relatively narrow bandwidth. For this purpose, the PDCP layer reduces the size of an IP packet header which is relatively great in size and includes unnecessary control information, namely, a function called header compression is performed.
A Radio Resource Control (RRC) layer located at the lowest portion of the third layer is only defined in the control plane. The RRC layer controls logical channels, transport channels and physical channels in relation to establishment, re-configuration and release of Radio Bearers (RBs). Here, the RB signifies a service provided by the second layer for data transmissions between the terminal and the E-UTRAN. If an RRC connection is established between the RRC layer of the terminal and the RRC layer of the radio network, the terminal is in the RRC connected mode. Otherwise, the terminal is in an RRC idle mode.
A Non-Access Stratum (NAS) layer located at an upper portion of the RRC layer performs functions, such as session management, mobility management and the like.
One cell constructing an eNB is set to one of bandwidths of 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 20 MHz and the like, so as to provide downlink or uplink transmission services to multiple terminals. Here, different cells may be set to provide different bandwidths.
Downlink transport channels for transmitting data from a network to a terminal may comprise a Broadcast Channel (BCH) for transmitting system information, a Paging Channel (PCH) for transmitting paging messages and a downlink Shared Channel (SCH) for transmitting other user traffic or control messages. Traffic or control messages of a downlink point-to-multipoint service (multicast or broadcast service) may be transmitted either via a downlink SCH, or via a separate downlink Multicast Channel (MCH). In addition, uplink transport channels for transmitting data from a terminal to a network may comprise a Random Access Channel (RACH) for transmitting an initial control message and an uplink Shared Channel (SCH) for transmitting user traffic or control messages.
Logical channels which are located at an upper portion of transport channels and mapped to the transport channels include a Broadcast Control Channel (BCCH), a Paging Control Channel (PCCH), a Common Control Channel (CCCH), a MBMS point-to-multipoint Control Channel/Multicast Control Channel (MCCH), a MBMS point-to-multipoint Traffic Channel/Multicast Traffic Channel (MTCH), and the like.
FIG. 3 shows a transmission on a control channel according to the related art.
A physical channel is composed of multiple sub-frames arranged on a time axis and multiple sub-carriers arranged on a frequency axis. Here, a single sub-frame includes a plurality of symbols on the time axis. One sub-frame is composed of a plurality of resource blocks, each of which includes a plurality of symbols and a plurality of subcarriers. Also, each sub-frame can use particular sub-carriers of particular symbols (e.g., a first symbol) at the corresponding sub-frame for a Physical Downlink Control Channel (PDCCH), namely, a L1/L2 control channel. One sub-frame is a time duration of 0.5 ms. A Transmission Time Interval (TTI) as a unit time for which data is transmitted is 1 ms corresponding to two sub-frames.
FIG. 4 is a block diagram of a network structure for a cell broadcast service. As illustrated in FIG. 4, CBS messages originate in a plurality of cell broadcast entities (hereinafter abbreviated CBEs) connected to a cell broadcast center (hereinafter abbreviated CBC). The CBE separates the CBS message into a plurality of pages. The CBC is one node of a core network that performs a scheduling function by managing the CBS message. Iu-BC is an interface defined between the CBC and the RNC using a service area broadcast protocol (hereinafter abbreviated SABP). The CBC can give the RNC a broadcast order for a new message or enable a previous broadcast message to be modified or terminated using the SABP. The RNC performs a scheduling function for a CBS message delivered by the CBC and a broadcasting function to transmit the message to a specific cell using a BMC protocol. The RNC has a broadcast/multicast inter-working function (hereinafter abbreviated BMC-IWF) above a BMC layer to perform an interpreting function for a message and information delivered from the CBC. The UE receives a CBS message broadcast by the UTRAN. Examples of BMC messages used in the BMC protocol are a CBS message delivering user information, a schedule message facilitating reception of a CBS message by a UE and a CBS41 message delivering a short message delivered from an ANSI41 network. All the messages are transmitted from the UTRAN to the UE in uni-direction through a logical channel such as CTCH (Common Traffic Channel). The UE can reduce its battery consumption by performing a discontinuous reception (hereinafter abbreviated DRX) using information in the schedule message transmitted by the UTRAN through CTCH (Common Traffic Channel).
In a related art, a Multimedia Broadcast/Multicast Service (MBMS) dedicated cell has been utilized only to provide the MBMS service. The MBMS dedicated cell provides point-to-multipoint channels for the MBMS service. However, the MBMS dedicated cell does not provide a unicast service (i.e., voice/video call between two end users) and does not provide an uplink channel. Further, in the MBMS dedicated cell, only minimal downlink control channel is provided except for channels for the MBMS service. Therefore, in the related art, the terminal can not receive a warning message when the terminal is camped on the MBMS dedicated cell, thusly causing a great drawback.